Sodium Carbonate is Saltier Than Sodium Chloride to Sodium-Depleted Rats

Abstract

In a series of behavioral experiments in the 1960s, G.R. Morrison identified several unique features of the taste of Na₂CO₃ to rats; namely, it is 1) considerably more intense than NaCl at isomolar concentrations, 2) avoided at 10 times lower concentrations than NaCl to thirsty rats, 3) preferred at 10 times lower concentrations than NaCl in sodium-depleted rats. He also demonstrated its qualitatively similarity to NaCl. In Experiment 1, we confirmed and extended many of Morrison's observations. Rats were injected with furosemide on 3 occasions to stimulate a sodium appetite. After each depletion, rats were given a brief-access taste test in a lickometer presenting, in random order, water and 7 concentrations of salt. One test used NaCl (0.028–0.89 M, quarter log steps), another used Na₂CO₃, and the third used Na₂CO₃, but at a tenfold lower concentration range (0.0028–0.089 M). Rats licked NaCl in an inverted-U shaped concentration-response function peaking at 0.158–0.281 M. As Morrison's results predicted, rats licked Na₂CO₃ in nearly identical fashion, but at a tenfold lower concentration range (peak at 0.0158–0.028 M). In a second experiment, furosemide-treated rats were repeatedly tested with the lower Na₂CO₃ range but mixed in the epithelial sodium channel blocker amiloride at various concentrations (3–300 μM, half log steps). Amiloride reduced licking for Na₂CO₃ and shifted the peak response rightward up to about half a log unit. Thus, this "super-saltiness" of Na₂CO₃ to rats is at least partly amiloride-dependent.

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